1. Field of the Invention
The present invention relates to a vehicle air conditioning system in which the operation mode of a refrigeration cycle is set to any one of several operation modes, i.e., a cooling mode, a heating mode, or a dehumidifying mode, in accordance with a target blowing temperature set by at least the temperature deviation between a set point temperature and an inside air temperature.
2. Description of the Related Art
Vehicle air conditioning systems are known in which an evaporator serving as a cooling heat exchanger for cooling air and a condenser serving as a heating heat exchanger for heating air are disposed inside an air duct with an external heat exchanger disposed externally to the air duct and coupled between the condenser and the evaporator. The vehicle air conditioning system is designed such that selecting a dehumidifying mode as an operation mode of the refrigeration cycle (heat pump cycle) will cause a refrigerant discharged from a discharge outlet of a compressor (refrigerant compressor) to circulate along a path from the condenser through a heating electronic expansion valve (a first variable throttle valve), an external heat exchanger, a cooling electronic expansion valve (a second variable throttle valve), an evaporator, and an accumulator to a compressor.
The combination of the degrees of opening of the heating and cooling electronic expansion valves during a dehumidifying mode are corrected according to five types of opening patterns that are set in accordance with a condenser outlet air temperature indicative of information regarding the blowing temperature of conditioned air blown through the air duct into a passenger compartment. In a dehumidifying mode, this allows for reducing the temperature deviation between an actual blowing temperature of conditioned air blown through the air duct into the passenger compartment and the target blowing temperature, resulting in improved control characteristics of the blowing temperature (e.g., see Japanese Patent Laid-Open Publication No. Hei 8-40056 (1996), essentially pages 9 to 11, FIGS. 11 to 16).
However, in the Hei 8-40056 vehicle air conditioning system, the degree of opening of the heating and cooling electronic expansion valves is varied in accordance with the condenser outlet air temperature indicative of information regarding the blowing temperature of conditioned air blown into the passenger compartment through the air duct. Thus, the degrees of opening of the heating and cooling electronic expansion valves are not corrected so as to control the cycle efficiency of the refrigeration cycle. Accordingly, in a wide range of airflow from a low airflow region during an intermediate period to a high airflow region at a relatively low outside air temperature (at about 10° C. of outside air), it was not possible to control the heat application capacity (heating capacity) of a heating heat exchanger and the cooling capacity (dehumidifying capacity) of a cooling heat exchanger to a target value while providing control to the cycle efficiency of the refrigeration cycle.
It is therefore an object of the present invention to provide a vehicle air conditioning system that enables the cycle efficiency of a refrigeration cycle to be controlled in a wide range of airflow from a low airflow region during an intermediate period to a high airflow region. It is also an object of the present invention to provide a vehicle air conditioning system which can control the heat application capacity (heating capacity) of a heating heat exchanger and the cooling capacity (dehumidifying capacity) of a cooling heat exchanger to a target value, while controlling the cycle efficiency of the refrigeration cycle, in a wide range of airflows from a low airflow region during an intermediate period to a high airflow region.